Plasma source with integral blade and method for removing materials from substrates

ABSTRACT

An atmospheric pressure plasma source includes a body including a distal end, a blade extending from the distal end and terminating at a blade edge, a plasma-generating unit, and a plasma outlet communicating with the plasma-generating unit and positioned at the distal end. The plasma outlet is oriented at a downward angle generally toward the blade edge, wherein the plasma outlet provides a plasma path directed generally toward the blade edge. The plasma may be applied to the coating at an interface between the coating and an underlying substrate. While applying the plasma, the blade is moved into contact with the coating at the interface, wherein the blade assists in separating the coating from the substrate while one or more components of the coating react with energetic species of the plasma.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/150,795, filed Feb. 8, 2009, titled “COATINGREMOVAL DEVICE AND METHODS”, the content of which is incorporated byreference herein in its entirety.

TECHNICAL FIELD

The present invention generally relates to the removal of materials fromsubstrates utilizing atmospheric pressure plasma.

BACKGROUND

Atmospheric pressure (AP) plasma may be utilized to remove a coating ofmaterial (or layer, film, paint, etc.) from the surface of a substrate.The source of the AP plasma may be a device configured to discharge anAP plasma plume from a nozzle. The device may positioned at somespecified distance between the nozzle and the surface of the coating,and oriented so as to direct the AP plasma plume toward the coating.While the AP plasma plume is active, the device may be moved across thecoating along an appropriate path. Alternatively, other types ofnon-plasma chemical etchants (e.g., wet etchants) may be employed toremove the coating from a substrate. Conventionally, the plasma or otherchemical etchant is utilized to attack the coating in a top-down removalprocess, i.e., starting with exposure to the uppermost (exposed) surfaceof the coating and etching/removing in the downward direction of thethickness of the coating until the underlying substrate is reached. Thetop-down removal process may be effective in many applications, but ishampered by the fact that all of the coating (its entire volume andthickness) must be etched in order to reach the substrate and completelyremove the coating from the substrate. This may take considerable timedepending on the thickness of the coating and the relative etch rate ofthe plasma or chemical etchant.

Another known technique for removing a coating from a substrate involvesutilizing a physical scraper or blade to delaminate the coating layerfrom the substrate. However, physical cutting or scraping is oftenconsidered inferior to plasma- and etchant-based techniques. Forinstance, this technique may be ineffective if the force of the bladeimpinging on the coating fails to overcome the strength of the adhesivebond strength of the coating to the substrate. The coating may alsoflake off or shear in the bulk of the coating layer, leaving behind apartially removed coating of uneven profile. The use of intense pressureon the blade may lead to damage to the substrate and may still leavebehind coating residue.

In view of the foregoing, there is a need for improved apparatus andmethods for efficiently and effectively removing various types ofmaterials from substrates without being impaired by problems attendingknown techniques.

SUMMARY

To address the foregoing problems, in whole or in part, and/or otherproblems that may have been observed by persons skilled in the art, thepresent disclosure provides methods, processes, systems, apparatus,instruments, and/or devices, as described by way of example inimplementations set forth below.

According to one implementation, an atmospheric pressure plasma sourceincludes a body including a distal end, a blade extending from thedistal end and terminating at a blade edge, a plasma-generating unit,and a plasma outlet communicating with the plasma-generating unit andpositioned at the distal end. The plasma outlet is oriented at adownward angle generally toward the blade edge, wherein the plasmaoutlet provides a plasma path directed generally toward the blade edge.

According to another implementation, a method is provided for removing acoating from a substrate on which the coating is disposed. A plasma isgenerated at atmospheric pressure. The plasma includes an energeticspecies reactive with one or more components of the coating. The plasmais applied as a plasma plume to the coating at an interface between thecoating and the substrate. While applying the plasma, a blade is movedinto contact with the coating at the interface, wherein the bladeassists in separating the coating from the substrate while the one ormore components of the coating react with the energetic species.

Other devices, apparatus, systems, methods, features and advantages ofthe invention will be or will become apparent to one with skill in theart upon examination of the following figures and detailed description.It is intended that all such additional systems, methods, features andadvantages be included within this description, be within the scope ofthe invention, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood by referring to the followingfigures. The components in the figures are not necessarily to scale,emphasis instead being placed upon illustrating the principles of theinvention. In the figures, like reference numerals designatecorresponding parts throughout the different views.

FIG. 1 illustrates an example of utilizing a conventional AP plasmasource in a conventional top-down material removal technique.

FIG. 2 is a diagram of an example of an AP plasma application systemaccording to implementations disclosed herein.

FIG. 3 is a detailed view of the region designated “A” in FIG. 2surrounding the coating-substrate interface.

FIG. 4 is a front perspective view of the front portion of the exampleof the AP plasma source illustrated in FIG. 2.

FIG. 5 is a side elevation view of an example of an AP plasma sourceaccording to another implementation.

FIG. 6 is a front perspective view of the front portion of the AP plasmasource illustrated in FIG. 5.

FIG. 7 is a side elevation view of an example of an AP plasma sourceaccording to another implementation.

FIG. 8 is a front perspective view of the front portion of the AP plasmasource illustrated in FIG. 7.

FIG. 9 is a side elevation view of an example of an AP plasma sourceaccording to another implementation.

FIG. 10 is a front perspective view of the front portion of the APplasma source illustrated in FIG. 9.

FIG. 11 is a side elevation view of an example of an AP plasma sourceaccording to another implementation.

FIG. 12 is a front perspective view of the front portion of the APplasma source illustrated in FIG. 11.

FIG. 13 is a plan view, in partial cross-section, of the AP plasmasource illustrated in FIGS. 11 and 12.

FIG. 14 is a front perspective view of the front portion of an AP plasmasource according to another implementation.

FIG. 15 is a front perspective view of the front portion of an AP plasmasource according to another implementation.

FIG. 16 is a front perspective view of the front portion of an AP plasmasource according to another implementation.

FIG. 17 is a side elevation view of an example of an AP plasma sourceaccording to another implementation.

FIG. 18 is a side elevation view of another example of an AP plasmasource according to another implementation.

FIG. 19 is a front perspective view of the front portion of the APplasma source illustrated in FIG. 18.

DETAILED DESCRIPTION

As used herein, the term “plasma” generally refers to a (partially)ionized gas-like mass comprising a mixture of ions, electrons andneutral species. The term “atmospheric pressure,” in the context of“atmospheric pressure plasma,” is not limited to a precise value ofpressure corresponding exactly to sea-level conditions. For instance,the value of “atmospheric pressure” is not limited to exactly 1 atm.Instead, “atmospheric pressure” generally encompasses ambient pressureat any geographic location and thus may encompass a range of values lessthan and/or greater than 1 atm as measured at sea level. Generally, an“atmospheric pressure plasma” is one that may be generated in an open orambient environment, i.e., without needing to reside in apressure-controlled chamber or evacuated chamber.

As used herein, a “non-thermal plasma” generally refers to a plasmaexhibiting a low energy density (relative to a “thermal” plasma) and ahigh electron temperature relative to the temperature of the surroundinggas. A non-thennal plasma is distinguished from a thermal plasma in thata thermal plasma exhibits a high energy density and both high electrontemperatures and high gas temperatures.

As used herein, the term “coating” generically refers to any materialdesired to be removed from an underlying substrate. The term “coating”is used interchangeably with like terms such as layer, film, paint, etc.

As used herein, the term “substrate” generically refers to any structurethat includes a surface on which a coating has been applied. Thesubstrate may present a surface having a simple planar or curvedgeometry or may have a complex or multi-featured topography.

For purposes of the present disclosure, it will be understood that whena layer (or coating, film, region, substrate, component, device, or thelike) is referred to as being “on” or “over” another layer, that layermay be directly or actually on (or over) the other layer or,alternatively, intervening layers (e.g., buffer layers, transitionlayers, interlayers, sacrificial layers, etch-stop layers, masks,electrodes, interconnects, contacts, or the like) may also be present. Alayer that is “directly on” another layer means that no interveninglayer is present, unless otherwise indicated. It will also be understoodthat when a layer is referred to as being “on” (or “over”) anotherlayer, that layer may cover the entire surface of the other layer oronly a portion of the other layer. It will be further understood thatterms such as “formed on” or “disposed on” are not intended to introduceany limitations relating to particular methods of material transport,deposition, fabrication, surface treatment, or physical, chemical, orionic bonding or interaction. The term “interposed” is interpreted in asimilar manner.

According to some implementations disclosed herein, an AP plasma sourceis configured for coating removal operations, including for example theremoval of polymeric coatings, paints, or the like from substrates orstructures of any type. The AP plasma source is configured to exhibitexceptionally high etching rates with minimal transfer of heat to theunderlying substrate. The AP plasma source generates one or more plasmaplumes or jets that include one or more energetic, chemically reactivespecies of a type effective for removing a coating composition ofinterest. The AP plasma source additionally includes a blade (orscraper, etc.) that includes a blade edge constructed of a non-marringmaterial. The plasma plumes and/or associated components utilized forplasma generation are positioned adjacent to, or embedded in, thenon-marring blade. In some implementations, the AP plasma source isconfigured such that the blade and/or the components involved ingenerating or directing the plasma are easily replaceable. Thenon-marring blade effects physical lifting, separating and/orundercutting at the coating-substrate interface while the AP plasmachemically etches the coating at the interface and promotes rapiddebonding at the interface. Accordingly, the AP plasma source effectsmaterial removal by way of a dual modality, one being the chemical(e.g., oxidizing) interaction of the activated plasma species of theplasma plume with the coating and the other being the physicalinteraction of the blade of the AP plasma source with the coating. Asnoted above, conventional plasma etching techniques must etch the fullvolume of the coating in order to remove the coating from the substrate.By contrast, the AP plasma sources and methods disclosed herein overcomethis limitation by attacking the coating only at (and immediatelyproximate to) the interface. In this manner, the AP plasma source isable to greatly enhance the removal rate because the plasma etches thecoating material only at the interface instead of etching the bulk ofthe material.

FIG. 1 illustrates an example of utilizing a conventional AP plasmasource in a conventional top-down material removal technique.Specifically, FIG. 1 illustrates a nozzle 110 of the conventional APplasma source (not shown) applying a plasma plume 114 to a typicalcoated structure 118. The coated structure 118 generally includes asubstrate 122 and a coating or layer 124 of material desired to beremoved cleanly from the substrate 122 without damaging the substrate122. The conventional plasma plume 114 is shown interacting with a topsurface 126 of the coating 124 and must interact with the entire volumeof the coating 124 to remove it from the underlying substrate 122.

FIG. 2 is a diagram of an example of an AP plasma application system 200according to implementations disclosed herein. The system 200 generallyincludes an AP plasma source 204 (or device, applicator, apparatus,instrument, pen, gun, etc.), a plasma-generating gas supply source 208,and a power source 212. The AP plasma source 204 generally includes amain body 216 (or support structure, housing, etc.) which may beconfigured for manual use (i.e., handheld) or automated use (e.g.,attached to a multi-axis robotics system, not shown). For manualoperations, a portion of the main body 216 may be utilized as a handle218. The AP plasma source 204 further includes a plasma outlet. In thepresent implementation, the plasma outlet is provided in the form of oneor more nozzles 222 at or extending out from a distal end 226 of themain body 216, and from which one or more plumes or jets 230 of APplasma are generated according to various implementations disclosedherein. The plasma-generating gas supply source 208 is in fluidcommunication with one or more gas inlets 234 of the AP plasma source204 by any suitable conduit and fittings for supplying a suitableplasma-generating gas to the AP plasma source 204. In one example, theplasma-generating gas is air, in which case the plasma-generating gassupply source 208 may be a source of low-pressure compressed air. In thecase of an air plasma, the plasma-generating gas supply source 208 mayalso serve as the source of active species of the AP plasma (e.g.,oxygen- and nitrogen-based species). Alternatively, one or more reactivegas supply sources 238 may also be placed in communication with the APplasma source 204 for such purposes as enhancing the supply of O₂ or N₂or for supplying other types of reactive species (e.g., He, Ar, othernoble gases, halogens, NH₃, CO₂, various hydrocarbons, etc.).

The power source 212 is in electrical communication with the AP plasmasource 204 by any suitable conduit 242 (e.g., wiring) and connectors forsupplying electrical power according to operating parameters suitablefor generating and maintaining a stable AP plasma. In some embodiments,the conduit 242 represents a single conduit that encloses both theelectrical wiring and the gas feed conduit(s) from the gas source(s)208, 238. In FIG. 2, the power source 212 represents the electronics anduser controls needed for this purpose. As appreciated by persons skilledin the art, the user controls may be configured as necessary to enablethe setting and adjustment of various operating parameters of thevoltage or current signal fed to the AP plasma source such as, forexample, power level, drive voltage amplitude, drive frequency, waveformshape, etc. Electrical signals of AC (e.g., RF), DC, pulsed DC, orarbitrary periodic waveforms with or without a DC offset may be utilizedto drive the AP plasma as appropriate for a particular application.Generally, the AP plasma source 204 may include any internal componentssuitable for generating a stable AP plasma that is subsequentlydischarged from the nozzle. In the present example, the AP plasma source204 is diagrammatically shown as including a plasma-generating unit ormodule 246 in the main body 216. The plasma-generating unit 246 mayinclude a powered or “hot” electrode 248 extending into aplasma-generating chamber 250 in fluid communication with the gas inlets234. The plasma-generating chamber 250 serves as a ground electrode forgenerating plasma and as a conduit for containing and flowing gases andplasma. In operation, the plasma is generated in an electric and/ormagnetic field established between the hot electrode 248 and the chamber250 and subsequently flows with the gas flow toward the nozzle 222. Ifthe AP plasma source includes more than one nozzle 222, each nozzle 222may include its own plasma generating unit 250.

As further illustrated in FIG. 2, the AP plasma source 204 includes ascraper or blade 254 extending out from the distal end 226 of the mainbody 216 below the nozzle 222 and the plasma plume 230. The thickness ofthe blade 254 tapers down to a distal blade edge 258 (i.e., the leadingedge of the blade 254). In some implementations, the blade 254 isadjoined to the main body 216 so as to be easily attachable to anddetachable from the main body 216, for cleaning, replacement, etc. Forexample, the blade 254 may be attached to the main body 216 by suitablefasteners (not shown). In the illustrated example, the blade 254 extendsout from the main body 216 farther than the nozzle 222. The blade 254may extend out to a distance somewhat greater than the expected lengthof the plasma plume 230, or alternately may be shorter than or terminateat about the same point or line as the end region of the plasma plume230. Also in this example, the nozzle 222 is oriented at an acute anglerelative to the blade 254 such that plasma plume 230 is directed towardthe blade edge 258, whereby the blade edge 258 and the distal-mostregion of the plasma plume 230 are both focused at the same point orline in front of the AP plasma source 204. The distal-most region of theplasma plume 230 is also referred to herein as the “plasma front.”

The blade 254 may be fabricated from a material that will not scratch,mar or otherwise damage the material of the substrate of the coatedstructure to which the plasma plume 230 and blade 254 are applied. Theparticular material selected for the blade 254 may depend on the type ofsubstrate contemplated. As examples, an aluminum blade may be utilizedon a substrate made of steel or other material significantly harder thanaluminum. A steel blade may be utilized on a glass or hard stonesubstrates. A magnesium or beryllium blade may be utilized on analuminum substrate. In other applications, the blade 254 may be composedof a composite material that may include fiberglass, carbon fiber, orother suitable composite. Aramids, polyamides, polyimides and otherhigh-temperature plastics may be utilized. Machinable ceramics such asMykroy® or Macor® may be utilized. Another example issilicone-impregnated fiber composites. Yet another example is Ryton®,which is a highly loaded, high-temperature, injection-moldablepolyphenylene sulfide plastic. Vespel® may also be utilized. Vespel® andRyton® are examples of polymers exhibiting good resistance to plasma.

FIG. 2 further illustrates an example of applying the AP plasma source204 to a coated structure 118. FIG. 3 is a detailed view of the regiondesignated “A” in FIG. 2 surrounding the coating-substrate interface. Nospecific limitations are placed on the type of coated structure 118 towhich the AP plasma source 204 is applicable. Generally, the coatedstructure 118 includes a substrate 122 and a coating 124 disposed in anyfixed manner (e.g., adhered, baked, cured, bound, painted, etc.) on theunderlying substrate 112. The substrate 122 may have any composition,e.g., metallic, polymeric, ceramic, etc. Moreover, generally nolimitation is placed on the type or composition of the coating 124 to beremoved. The coating 124 will generally be one in which at least some ofthe components are responsive to active species of the AP plasma. Suchcoatings 124 may include, for example, various types of polymericcoatings and paints. Generally, no limitation is placed on the thicknessof either the substrate 122 or the coating 124. Moreover, the substrate122 and associated coating 124 are not required to have a simple planaror curvilinear geometry. Instead, the AP plasma source 204 is effectivefor treating three-dimensional topographies, irregular profiles, andcomplex geometries. The AP plasma source 204 may be utilized to applythe plasma plume 230 around structural features such as, for example,rivets, or inside narrow channels, or in corners or cracks, etc.

It will also be understood that a “material,” “coating,” “layer,” “film”or the like as used herein encompasses single-layer, multi-layered orcomposite materials. For instance, a given polymeric material mayinclude a protective overcoat, an adhesion-promoting layer, or the like.A paint may include a primer layer, a topcoat, etc. The AP plasma source204 is effective for all such layers or strata of a multi-layeredmaterial down to the underlying substrate 122. The AP plasma source 204may also be utilized to precisely remove one or more selected layers ofa multi-layered material, leaving underling layers intact on thesubstrate 122.

In operation, the AP plasma source 204 is moved toward the coatedstructure 118 (or, equivalently, the coated structure 118 is movedtoward the AP plasma source 204) such that the blade 254 and plasmaplume 230 encounter the interface (or bond line) between the substrate122 and the coating 124. It will be noted that in many situations, aninterface is not initially exposed, in which case the AP plasma source204 may first be operated to etch down through the coated structureuntil the interface is exposed. In the illustrated example in which theblade 254 extends out from the main body 216 of the AP plasma source 204at a greater distance than the plasma plume 230, the blade edge 258 mayencounter the interface first. However, as noted above the plasma outlet(in the present implementation, the nozzle 222) of the AP plasma source204 may be oriented so as to provide a plasma path in a plasma flowdirection 302 directed generally toward the blade edge 258. That is, theplasma outlet is oriented such that the plasma plume 230 is focusedgenerally toward the blade edge 258 and thus preferentially directed atthe interface along with the blade edge 258. This configuration isadvantageous because the volume of the coating 124 being etched per unitarea of removed coating 124 is much greater compared to a conventionaltop down etching process. The energetic species of the plasma plume 230etch away the coating 124 at the interface (preferably without damagingthe substrate 122) according to any mechanism or reaction dependent onthe energetic species and the material being etched. For instance,oxygen-based species may react with polymeric components of the coating124 to synthesize carbon dioxide and/or water vapor. While the plasmaplume 230 etches the coating 124, the blade 254 is moved into the coatedstructure 118 at the interface so as to assist in separating and liftingthe coating 124 from the underlying substrate 122. It thus can be seenthat the entire thickness of the coating 124 may be removed from thesubstrate 122 without requiring that the entire volume of the coating124 be subjected to the plasma plume 230 as in conventional techniques.That is, only a fraction of the coating 124, at the interface with thesubstrate 122, needs to actually interact with the plasma plume 230.

The plasma generated by the AP plasma source 204 may be a cold, ornon-thermal, plasma containing one or more reactive species suitable forchemically interacting with the coating 124 in a manner sufficient forcausing the coating 124 to be removed from its underlying substrate 122.Generally, the reactive species may include photons, metastable species,atomic species, free radicals, molecular fragments, monomers, electrons,and ions. The reactive species desired to be produced will generallydepend on the type of coating 124 to be removed. In the case of variouspolymeric coatings and paints, a highly oxidizing plasma has been foundto be effective, in which case the predominant reactive species mayinclude O, O₂* (the asterisk designating the metastable form of diatomicoxygen), and/or O₃. In various implementations, air supplied by theplasma-generating gas supply source 208 may be sufficient for generatingan effective amount of oxygen-based energetic species for removingvarious types of polymeric coatings or paints. Additional non-limitingexamples of active species that may be formed in the plasma and utilizedfor material removal include fluorine, chlorine, bromine, iodine,nitrogen, or sulphur. One or more of these species may be utilized, forexample, to selectively etch (or enhance the etching selectivity of) aprimer layer or adhesion layer whether or not a specialized chemistry orprimer formulation has been employed in the coated structure. Forexample, in the case of a primer that exhibits preferential etching byoxygen, oxygen species could be used so that the primer layer ispreferentially etched relative to a topcoating layer. The oxidizer mayalso be mixed with an inert gas or relatively inert gas such as nitrogenor natural air mixtures. It is also possible to use reducing plasmaspecies such as hydrogen or ammonia. It is also possible to use neutralor inert gases to energetically bombard the interface layer and promotedecohesion at the bond line. The type of oxidizing species in the plasmaplume 230 may be adjusted for specific coating chemistries to maximizethe etch rate of the coating 124. For instance, certain coatingchemistries may be quite resistant to an oxygen-containing oxidizer butcould be quite easily etched by a fluorinated oxidizer.

As an example demonstrating the effectiveness of the present teachings,consider a coated structure comprising a coating that is 0.125 inchthick over a 12-inch by 12-inch panel (area=144 in²). If a conventional,top-down process is employed to remove this coating, then the volume ofmaterial that must be etched is 12-inch×12-inch×0.125-inch=18 in³. Bycontrast, the AP plasma source 204 disclosed herein would attack andetch this coating only at its interface with the underlying panel, andwould likely need to etch only 0.005 inch of the coating thickness atthe interface, which would equate to 12-inch×12-inch×0.005-inch=0.72 in³of material etched. Assuming the volumetric etch rate of the AP plasmasource 204 remains constant throughout the coating removal process, thenetching the same 144 in² area would require only 1/24th of the time tocompletely remove the coating as compared to the conventional top-downtechnique.

Generally, operating parameters associated with the AP plasma source 204are selected so as to produce a stable plasma discharge. The operatingparameters will depend on the particular application, which may range,for example, from nanoscale etching of micro-fabricated structures ordevices (e.g., MEMS devices) to removing large areas of paint fromaircraft carriers. Examples of operating parameters will now be providedwith the understanding that the broad teachings herein are not limitedby such examples. Generally gas feed rates and pressures will depend onthe type of source gases employed. In the case of generating an airplasma, the rate at which the air is fed to the AP plasma source 204 mayrange from 1×10⁻⁶ SCCM to 1×10⁶ SCCM. The feed pressure into the APplasma source 204 may range from 1 Pa to 1×10⁷ Pa. The power level ofthe electrical field driving the plasma may range from 1×10⁻⁶ W to 1×10⁶W. The drive frequency of the electrical field may range from DC (0 GHz)to 100 GHz. The foregoing parameters may depend on the composition andthickness of the material to be removed as well as the intended scale(nanoscale vs. macroscale) on which the removal process is planned to beperformed.

FIG. 4 is a front perspective view of the front portion of the exampleof the AP plasma source 204 illustrated in FIG. 2. In this example, theAP plasma source 204 includes a plurality of nozzles 222 arranged in alinear series along the width of the main body 216, spaced apart fromeach other and positioned above the blade 254. Accordingly, the APplasma source 204 emits a corresponding number of plasma plumes 230.Each nozzle 222 may communicate with a respective plasma-generating unit246 (i.e., electrode 248 and plasma-forming chamber 250) housed in themain body 216. As also shown in FIG. 4, the plasma plume or plumes 230flow along a plasma path 402 in a direction generally toward the bladeedge 258. By “generally” is meant that the plasma path 402 is notrequired to exactly intersect the blade edge 258. The angle of theplasma path 402 may be such that the plasma path 402 encounters theblade 254 at a point or line short of the blade edge 258, or passes theplane of the blade 254 at a point or line beyond the blade edge 258. Asfurther shown in FIG. 4, the blade 254 or at least the blade edge 258has a blade width in a direction transverse to the direction in whichthe plasma path 402 runs (i.e., the flow direction of the plasma path402). The blade width may be defined as extending between opposinglateral sides 406, 408 of the blade 254. The plasma plume 230established by the plasma outlet—or in the present implementation thecollection of plasma plumes 230 established by the linear series ofnozzles 222, which collectively form a plasma front—likewise has a widthin the transverse direction. The plasma outlet (e.g., the nozzles 222)may be configured such that the width of the resulting plasma plume 230is coextensive with (or spans) a substantial portion of the width of theblade edge 258.

FIG. 5 is a side elevation view of an example of an AP plasma source 504according to another implementation. FIG. 6 is a front perspective viewof the front portion of the AP plasma source 504 illustrated in FIG. 5.In this example, the main body 216 includes a plenum 562 (or manifold,chamber, etc.) communicating with a gas outlet 564 located at the distalend 226 above the nozzles 222. A dedicated gas 566 line may communicatewith the plenum 562 to supply air or other inert gas. Alternatively, theAP plasma source 504 may be configured to route a portion of theplasma-generating gas fed through the gas line utilized to supply theplasma-generating unit 246 to the plenum 562. As illustrated, thecross-sectional flow area of the gas outlet 564 may have an aspect ratioin which the width (transverse to the direction of flow) is the dominantdimension. That is, the gas outlet 564 in this example is shaped as aslot. By this configuration, the gas stream is emitted from the gasoutlet 564 as a gas curtain or air knife 568. As with the nozzles 222,the main body 216 may be configured such that the gas outlet 564, andthus the gas curtain 568, are angled toward the blade edge 258 such thatthe resulting gas path is directed generally toward the blade edge 258.The gas curtain 568 may be utilized to affect the shape of the output ofthe linear plasma plumes 230, thereby focusing the plasma into a narrowstream that may increase the removal rate of coating material at thecoating/substrate interface of a coated structure. This auxiliary gassupply may also assist in cooling the substrate during application ofthe plasma.

FIG. 7 is a side elevation view of an example of an AP plasma source 704according to another implementation. FIG. 8 is a front perspective viewof the front portion of the AP plasma source 704 illustrated in FIG. 7.In this example, the main body 216 includes a plenum 762 communicatingwith a gas outlet 764 located at the distal end 226 below the nozzles222 and above the blade 254. A dedicated gas line 766 may be connectedto the plenum 762 to supply air or other inert gas. Alternatively, aportion of the plasma-generating gas may be routed to the plenum 762 forthis purpose, as described above. The gas outlet 764 may be shaped as aslot. By this configuration, the gas stream is emitted from the gasoutlet 764 as a gas curtain or air knife 768 below the plasma. The gasoutlet 764 may be oriented such that the gas curtain 768 flows generallyparallel to the blade 254, or alternatively the gas curtain 768 may beangled relative to the blade 254. The gas curtain 768 may be utilizedfor the same purposes as described above in conjunction with FIGS. 5 and6.

FIG. 9 is a side elevation view of an example of an AP plasma source 904according to another implementation. FIG. 10 is a front perspective viewof the front portion of the AP plasma source 904 illustrated in FIG. 9.In this example, the main body 216 includes an upper plenum 562communicating with an upper gas outlet 564 located at the distal end 226above the nozzles 222, and a corresponding gas line 566, similar to theimplementation illustrated in FIGS. 5 and 6. The main body 216 alsoincludes a lower plenum 762 communicating with a lower gas outlet 764located at the distal end 226 below the nozzles 222 but above the blade254, and a corresponding gas line 766, similar to the implementationillustrated in FIGS. 7 and 8. Consequently, the plasma plumes 230 flowbetween an upper (or first) gas curtain 568 and a lower (or second) gascurtain 768. The gas curtains 568, 768 may be utilized for the samepurposes as described above in conjunction with FIGS. 5-8.

FIG. 11 is a side elevation view of an example of an AP plasma source1104 according to another implementation. FIG. 12 is a front perspectiveview of the front portion of the AP plasma source 1104 illustrated inFIG. 11. FIG. 13 is a plan view of the AP plasma source 1104 illustratedin FIGS. 11 and 12. In this example, the nozzles 222 are embeddedfurther into the main body 216 and communicate with respective angledplasma outlets 1222 (e.g., orifices) located at the distal end 226. Theplasma outlets 1222 are angled, not only downward relative to the blade254 but also laterally relative to the direction of blade movement(i.e., toward a coated structure). Stated in another way, one componentof the angle may be considered as being toward a lateral side 408 of theblade 254. FIG. 13 illustrates the orientation of the plasma plumes 230that results from this configuration. It can be seen that a part of the“lengths” of the plasma plumes 230 are now more closely projected on theplasma front that initially comes into contact with thecoating-substrate interface, and the plasma front is more contiguous asa plasma line rather individual plasma jets. This configuration may beuseful for enhancing the focus of the plasma toward the blade 254 andthe coating/substrate interface and for providing for uniform coverageby the plasma across the interface. The angled direction of the plasmaplumes 230 may be enhanced or accommodated by providing angled grooves1272 leading from the angled plasma outlets 1222.

FIG. 14 is a front perspective view of the front portion of an AP plasmasource 1404 according to another implementation. The AP plasma source1404 includes a plurality of plasma-generating units 246 as describedabove. In this implementation, a plenum in the main body 216interconnects the plasma-generating units 246 with a slot-shaped plasmaoutlet 1422. By this configuration, the respective plasma plumes emittedfrom the plasma-generating units 246 combine (or merge, coalesce, etc.)to form a “plasma line” 1430, i.e., a continuous, focused line of plasmadirected at the coating/substrate interface. Optionally, one or more ofthe plasma-generating units 246 or outlets thereof may be angled towardthe others to enhance the combination of the plasma plumes into thesingle plasma line 1430.

FIG. 15 is a front perspective view of the front portion of an AP plasmasource 1504 according to another implementation. The AP plasma source1504 is configured to emit a plasma line 1430 as just described inconjunction with FIG. 14. In addition, the AP plasma source 1504 isconfigured to emit an upper gas curtain 568 as described above inconjunction with FIGS. 5 and 6. Alternatively, the AP plasma source 1504may be configured to emit a lower gas curtain 768 as described above inconjunction with FIGS. 7 and 8.

FIG. 16 is a front perspective view of the front portion of an AP plasmasource 1604 according to another implementation. The AP plasma source1604 is configured to emit a plasma line 1430 as just described inconjunction with FIG. 14. In addition, the AP plasma source 1604 isconfigured to emit an upper gas curtain 568 and a lower gas curtain 768as described above in conjunction with FIGS. 9 and 10.

FIG. 17 is a side elevation view of an example of an AP plasma source1704 according to another implementation. The AP plasma source 1704 isconfigured to enable adjustment of the angle of the plasma plume 230relative to the blade 254. For example, a portion 1776 of the AP plasmasource 1704 that includes the nozzles 222 may be pivotable about atransverse axis provided by a structural member such as a yoke 1778supporting one or more pins 1780. The AP plasma source 1704 may includea mechanism for locking the pivotable portion 1776 in place at aselected angle. As one example, the AP plasma source 1704 may include abracket 1782 that moves with the pivotable portion 1776. A suitablefastener 1784 extends through a curved slot 1786 of the bracket 1782 andinto the main body 216. The fastener 1784 may be manipulated to bearagainst the bracket 1782 to prevent its movement, thereby locking theposition of the pivotable portion 1776 and fixing the angle of theplasma plume 230. This adjustable configuration may be useful fordifferent coating removal conditions, such as varying coatingthicknesses, curved surface topologies, etc.

In another implementation, a portion of the AP plasma apparatus such asits distal end region may be flexible or compliant. This may be usefulfor enabling the AP plasma apparatus to bend around or conform to curvedor complex surfaces.

FIG. 18 is a side elevation view of another example of an AP plasmasource 1804 according to another implementation. FIG. 19 is a frontperspective view of the front portion of the AP plasma source 1804illustrated in FIG. 18. The AP plasma source 1804 includes one or moreplasma-generating units 1846 in a main body 1816 communicating with oneor more nozzles (or a manifold) 1822. The nozzle(s) or manifold 1822 areset back in the main body 1816 and communicate with a slot-shaped plasmaoutlet 1824 that opens at a distal end 1826 of the main body 1316. Bythis configuration, the AP plasma source 1304 produces a wide,predominantly linear or horizontally-oriented plasma plume or “plasmaline” 1830 with wide, predominantly linear or horizontally-orientedshock waves or pressure waves 1832.

The generation of shock waves or pressure waves 1832 is described indetail in a copending U.S. patent application Ser. No. 12/702,039, filedFeb. 8, 2010, titled “PLASMA SOURCE AND METHOD FOR REMOVING MATERIALSFROM SUBSTRATES UTILIZING PRESSURE WAVES”, the content of which isincorporated by reference herein in its entirety. Briefly, thepressure-wave or shock-wave assisted plasma plume exhibits areas ofperiodically increasing (high) and decreasing (low) plasma density.Without wishing to be bound by any one particular theory, it ispostulated herein that this periodic plasma density contributes toenhanced removal rates, and that the plasma plume may be characterizedas exhibiting pressure waves or pressure fronts, which in someimplementations may be further characterized as shock waves or shockfronts that may be observed as supersonic shock diamonds or Mach disks.When the AP plasma source is operated to apply the plasma plume to amaterial to be removed, the shock waves (or other type of pressurewaves) generated in the plasma plume physically disrupt the looselyadhered build-up on the material. The as-generated shock wave orpressure wave interacts with the loosely adhered residue and the residueis consequently ejected from or blown off the surface. Accordingly, theAP plasma source in this case effects material removal by way of anotherdual modality, one being the chemical (e.g., oxidizing) interaction ofthe activated plasma species of the plasma plume with the coating andthe other being the physical interaction of the shock wave or pressurewave structures of the plasma plume with the coating. The AP plasmasource according to this implementation overcomes the limitations ofconventional techniques by enabling inorganic or other typicallyunresponsive components to be rapidly broken up or peeled away, therebycontinuously revealing fresh new surfaces of the coating for treatmentby the activated species of the plasma.

Certain pressure regimes, geometrical configurations, and otheroperational parameters will give rise to suitable plasma and shock wavegeneration and control. In one implementation, the nozzle is configuredto cause rapid expansion of the gas emanating therefrom. As an example,the nozzle may have a converging or converging-diverging configurationof appropriate dimensions. In this case, the AP plasma generated withinthe AP plasma source flows from the nozzle exit at supersonic velocityand at a pressure different from (less than or greater than) the ambientpressure outside the nozzle exit. Another example of a nozzle that maybe suitable is a non-axially symmetric nozzle such as an aerospikenozzle. In another implementation, the drive frequency and/or powerlevel applied by the power source to the electrical field generating theplasma are controlled so as to modulate the pressure waves (e.g.,compression waves) generated in the AP plasma source. Pressure wavesgenerated in such manner may be, or be similar to, acoustic shock wavesor pressure waves. Similarly, this may be accomplished inductively bygenerating a time-varying magnetic field to modulate the plasma. Inanother implementation, the geometry of the AP plasma source (e.g., thevolume and the length-to-width ratios of the nozzle and/or upstreamplasma-generating chamber) may be selected or adjusted so as toselectively filter or enhance certain frequency modes in the pressurewaves of the plasma. This may be analogous to causing acoustic gain orresonance to occur to further enhance the coherency of the shock waves.In another implementation, a piezoelectric material, such as for examplevarious known ceramics or polymers (e.g., barium titanate, leadzirconium titanate, polyvinylidene fluoride, etc.) may be driven by thepower source to produce vibrations or oscillations transferred to theas-generated plasma plume. In another implementation, the supply gaspressure to the plasma plume may be modulated in order to create thenecessary pressure waves or shockwaves by rapidly actuating a high speedgas valve. For example, a pneumatically actuated valve, electricallyactuated valve or piezoelectric valve actuator may be used to modulatethe pressure being fed into the AP plasma device.

In some implementations, pressure waves or shock waves may be producedby feeding air as a source gas to an AP plasma source of this type at apressure ranging from 30-110 psi and at a flow rate ranging from 1-7.5CFM. In another example, the pressure range is 65-95 psi. In anotherexample, the flow rate range is 1-4 CFM. Pressures higher than 110 psimay also be implemented to produce shock waves. In a more generalexample, the pressure may be 30 psi or greater and the flow rate may be1 CFM or greater. The AP plasma source may in these cases include aconverging or converging-diverging nozzle.

In the various implementations illustrated in FIGS. 2-19, the AP plasmaapparatus—whether outputting individual plasma plumes 230 or a singleplasma line 1430—provides a substantially uniform or contiguous plasmafront that may be focused, together with the blade edge 258, toward adesired coating-substrate interface. In some implementations such asillustrated in FIGS. 2-19, the width of the plasma front may be asubstantial portion of the width of the blade 254. By “substantial” ismeant that the width of the plasma front in this case ranges from atleast greater than half the width of the blade 254 up to equaling thewidth of the blade 254.

In the various implementations illustrated in FIGS. 2-19, the blade 254is shown as being a structure distinct from other components disposed inor supported by the main body 216 of the AP plasma source. It will beunderstood, however, that in any of these implementations the blade 254may be integrated with the main body 216 to a greater degree. Thus, oneor more portions of the body 216 illustrated in FIGS. 2-19 mayalternatively be considered as being a portion of the blade 254,depending on where the interface between the body 216 and the blade 254is defined. As an example, all or part of the plasma-generating units246 may be embedded within the portion of the main body 216 constitutingthe blade 254, with the nozzle(s) 222 or other type of plasma outlet(s)being positioned at the blade 254 and at, or at some distance from, theblade edge 258. In this case, the portion of the blade 254 that includesthe nozzles 222 or plasma outlets may be oriented such that the plasmaplume(s) 230 or plasma line 1430 is angled downward toward the bladeedge 258 in a manner similar to that described above as regards theother implementations.

In general, terms such as “communicate” and “in . . . communicationwith” (for example, a first component “communicates with” or “is incommunication with” a second component) are used herein to indicate astructural, functional, mechanical, electrical, signal, optical,magnetic, electromagnetic, ionic or fluidic relationship between two ormore components or elements. As such, the fact that one component issaid to communicate with a second component is not intended to excludethe possibility that additional components may be present between,and/or operatively associated or engaged with, the first and secondcomponents.

It will be understood that various aspects or details of the inventionmay be changed without departing from the scope of the invention.Furthermore, the foregoing description is for the purpose ofillustration only, and not for the purpose of limitation—the inventionbeing defined by the claims.

1. An atmospheric pressure plasma source, comprising: a body including adistal end; a blade extending from the distal end and terminating at ablade edge; a plasma-generating unit; and a plasma outlet communicatingwith the plasma-generating unit and positioned at the distal end, theplasma outlet oriented at a downward angle generally toward the bladeedge, wherein the plasma outlet provides a plasma path directedgenerally toward the blade edge.
 2. The atmospheric pressure plasmasource of claim 1, wherein the plasma outlet is disposed at a portion ofthe body above the blade edge.
 3. The atmospheric pressure plasma sourceof claim 1, wherein the plasma outlet is disposed at a portion of theblade above the blade edge.
 4. The atmospheric pressure plasma source ofclaim 1, wherein the blade edge has a blade width transverse to a flowdirection of the plasma path, and the plasma outlet is configured toproduce a plasma plume along the plasma path having a width coextensivewith a substantial portion of the blade width.
 5. The atmosphericpressure plasma source of claim 1, wherein the plasma outlet comprises aplurality of nozzles communicating with the respective plasma-generatingunits.
 6. The atmospheric pressure plasma source of claim 1, wherein theplasma outlet comprises a plurality of angled orifices communicatingwith the respective plasma-generating units and oriented at an angletoward a lateral side of the blade, wherein the angled orifices providecorresponding plasma paths from the plasma-generating units directedgenerally toward the blade edge and toward the lateral side.
 7. Theatmospheric pressure plasma source of claim 1, wherein the plasma outletcomprises a contiguous slot-shaped opening communicating with theplasma-generating units.
 8. The atmospheric pressure plasma source ofclaim 1, comprising a gas outlet positioned at the distal end above theplasma outlet and oriented at a downward angle generally toward theblade edge, wherein the gas outlet provides a gas path above the plasmapath and directed generally toward the blade edge.
 9. The atmosphericpressure plasma source of claim 1, comprising a gas outlet positioned atthe distal end below the plasma outlet and above the blade, wherein thegas outlet provides a gas path below the plasma path and directedgenerally toward the blade edge.
 10. The atmospheric pressure plasmasource of claim 1, comprising an upper gas outlet positioned at thedistal end above the plasma outlet and oriented at a downward anglegenerally toward the blade edge, and a lower gas outlet positioned atthe distal end below the plasma outlet and above the blade, wherein theupper gas outlet and the lower gas outlet provide a gas pathsrespectively above and below the plasma path and directed generallytoward the blade edge.
 11. The atmospheric pressure plasma source ofclaim 1, wherein the body includes a pivotable portion pivotablerelative to the blade and the plasma outlet is located at the pivotableportion, and wherein the angle of the plasma path relative to the bladeedge is adjustable.
 12. A method for removing a coating from a substrateon which the coating is disposed, the method comprising: generating aplasma at atmospheric pressure, the plasma comprising an energeticspecies reactive with one or more components of the coating; applyingthe plasma as a plasma plume to the coating at an interface between thecoating and the substrate; and while applying the plasma, moving a bladeinto contact with the coating at the interface, wherein the bladeassists in separating the coating from the substrate while the one ormore components of the coating react with the energetic species.
 13. Themethod of claim 12, wherein generating the plasma, applying the plasmaand moving the blade comprise operating a plasma source that comprisesthe blade and emits the plasma plume above the blade.
 14. The method ofclaim 12, wherein applying the plasma comprises emitting the plasma froma plurality of nozzles in a downward direction generally toward aleading edge of the blade.
 15. The method of claim 12, wherein applyingthe plasma comprises emitting the plasma as a wide plasma plume from aslot-shaped plasma outlet in a downward direction generally toward aleading edge of the blade.
 16. The method of claim 12, wherein the bladehas a blade width transverse to a flow direction of the plasma plume,and the plasma plume has a width coextensive with a substantial portionof the blade width.
 17. The method of claim 12, wherein applying theplasma comprises emitting the plasma in a downward direction generallytoward a leading edge of the blade and at an angle toward a lateral sideof the blade.
 18. The method of claim 12, comprising applying a gascurtain above or below the plasma plume and generally toward a leadingedge of the blade.
 19. The method of claim 12, comprising applying afirst gas curtain above the plasma plume and generally toward a leadingedge of the blade, and applying a second gas curtain below the plasmaplume and generally toward a leading edge of the blade.
 20. The methodof claim 12, comprising adjusting an angle of the plasma plume relativeto a leading edge of the blade.